Cross feed heads carrying radially positionable rotating cutting tools for performing facing as well as a variety of other operations are known in the prior art. Such cross feed heads have been adapted for attachment to various forms of horizontal boring mills and have been capable of performing facing, contouring and thread forming work. The primary advantage offered by cross feed heads is that large workpieces may remain essentially stationary during machining, thereby enhancing safety and permitting the simplification of work holding devices. Examples of prior art cross feed heads are described in U.S. Pat. Nos. 3,311,003; 3,744,352; 3,902,386; 4,250,775; and 4,250,777.
Prior art cross feed head arrangements, although capable of satisfactorily performing numerous machining operations, have inherent limitations. Prominent among such limitations is the available range of radial travel and the maximum angular velocity (RPM) at which the head can be rotated. The range of radial travel is necessarily limited by the size of the head, which typically has been of relatively small diameter. The maximum velocity at which the head can be rotated is dependent upon the degree of dynamic imbalance occasioned in the head when the tool carried thereby is in a given radial position. The prior art has recognized that a head, which is dynamically unbalanced and rotated at high speed, will engender vibrations which adversely affect the surface being machined. For example, the cross feed head disclosed in U.S. Pat. No. 3,824,883 has a pair of cutters arranged for simultaneous radial movement of equal distances in opposite directions in order to provide a cross feed head which is dynamically balanced.
The slides in prior art cross feed heads have been positioned by various drives. The drives include worm gear, rack and pinion and cam arrangements. A major problem with such prior art drives is that they do not afford the superior accuracy and minimal friction which is a characteristic of precision screw assemblies. The accurance of precision screw assemblies has been widely recognized in that they are typically employed to drive the slides of machine tools and are incorporated in many precision measuring machines.
Another drawback of exisitng cross feed heads is their lack of versatility owing to their specialized functions and the fact that they are essentially attachments to exisitng machines. For example, state of the art cross feed heads are not adapted to perform a drilling type operation but can only complete finishing work on an already machined bore. It would obviously be highly desirable, in order to minimize machining time, to bore and finish without the necessity for mounting a cross feed head attachment after the boring work is completed.